The present invention relates to a heat-developable photosensitive material, in particular, a heat-developable photosensitive material for scanners and image setters, which is suitable for photomechanical process. More specifically, the present invention relates to a heat-developable photosensitive material for photomechanical process, which can affords images of low fog, and little increase of fog and little fluctuation of sensitivity during storage before heat development as well as images with high Dmax (maximum density) suitable for use in photomechanical process.
A large number of photosensitive materials are known which have a photosensitive layer on a support and form image by imaging exposure. An example of a system that enables environmental conservation or simplification of image formation includes a technique of forming an image by heat development.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photomechanical processes from the standpoints of environmental protection and space savings. Techniques relating to heat-developable photosensitive materials for use in photomechanical processes are required which enables efficient exposure by a laser scanner or a laser image setter and formation of a clear black image having high resolution and sharpness. The heat-developable photosensitive materials can provide users with a simple and non-polluting heat development processing system which eliminates the use of solution-type processing chemicals.
Methods for forming an image by heat development are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, Imaging Processes and Materials, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, 8th ed., compiled by J.Sturge, V. Walworth and A. Shepp, Chapyer 9, p.279, Neblette (1969). The photosensitive material contains a reducible light-insensitive silver source (e.g., organic silver salt), a photocatalyst (e.g., silver halide) in a catalytically active amount, and a reducing agent for silver, which are usually dispersed in an organic binder matrix. This photosensitive material is stable at an ambient temperature, but when the material is heated at a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. Theoxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced by the reaction of the reducible silver salt in the exposure region provides a black image and this presents a contrast to the non-exposure region to form an image.
Such heat-developable photosensitive materials are practically used mainly in the field of microphotography and the medical field. However, they use a high development temperature of 100xc2x0 C. or higher and hence suffer from problems that slight change of development temperature or development time may cause fluctuation of performance, and they show poor image storability. Therefore, improvement has been desired.
On the other hand, low contrast heat-developable photosensitive materials have not been accepted in the field of graphic arts, since higher contrast is required in that field.
To overcome this problem, heat development techniques for affording ultrahigh contrast characteristics by using a nucleating agent have been disclosed in U.S. Pat. Nos. 5,496,695, 5,536,622, 5,545,515 and 5,635,339. However, in most of these photosensitive materials, a photosensitive layer is formed by applying a coating solution containing an organic solvent such as toluene, methyl ethyl ketone (MEK) or methanol as a solvent. However, use of an organic solvent as a solvent is not preferred because of its adverse effect on a human body during the production process or in view of the cost for recovery of the solvent and other process steps.
In addition, although the heat-developable photosensitive materials disclosed in the aforementioned patent documents, which have ultrahigh contrast characteristic, show good photographic performance under an optimum heat development condition, they suffer problems that slight change of environmental temperature or humidity, or development time or temperature may cause quick changes of maximum density (Dmax) and half tone dot percentage and raise of Dmin.
Accordingly, a method of forming a photosensitive layer by applying a coating solution containing a water solvent free of the aforementioned problems has been proposed (hereinafter referred to as xe2x80x9caqueous photosensitive layerxe2x80x9d). For example, JP-A-49-52626 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), JP-A-53-116144 and so forth describe use of gelatin as a binder, and JP-A-50-151138 describes use of polyvinyl alcohol as a binder.
Furthermore, JP-A-60-61747 describes use of gelatin and polyvinyl alcohol in combination. JP-A-58-28737 describes a photosensitive layer containing a water-soluble polyvinyl acetal as a binder.
In fact, when such a binder is used, a photosensitive layer can be formed using a coating solution comprising a water solvent, and this is advantageous in view of environmental protection and cost.
However, when a polymer selected from gelatin, polyvinyl alcohol, water-soluble polyacetal and so forth is used as a main binder, a coating obtained has a coated surface of which properties are not acceptable for practical use, because of the poor compatibility of the polymer with an organic silver salt. Moreover, blackening density in exposed areas becomes low and density in unexposed areas becomes high, and thus there are provided only images of which commercial value is seriously impaired.
Techniques for aqueous photosensitive material that are excellent in view of environmental protection and cost, and which can provide good coated surface property and ultrahigh contrast characteristics are disclosed in JP-A-10-10669, Japanese Patent Application Nos. 9-171750, JP-A-11-174621, JP-A-11-218877, JP-A-11-223900, JP-A-223902, JP-A-11-282128, and JP-A-11-295845. These techniques markedly improved the coated surface property and photographic performance. However, it is desired to further improve the performance in order to attain stable quality in the commercial market.
Further, a color photomechanical process is carried out by using four films for the four colors, i.e., Y, M, C and K. When these four films are simultaneously subjected to light exposure and heat development, any particular problem is not caused. However, the light exposure and the heat development are often performed on different occasions for these four films. In such a case, because the period after the heat development is different for each film, the sizes of the films may not fit to one another, which often causes color deviation.
In order to solve this problem, techniques utilizing a support having an undercoat layer containing a vinylidene chloride copolymer for heat-developable photosensitive materials are disclosed in JP-A-2000-39684 and Japanese Patent Application Nos. 10-355429. Although these techniques exhibit marked effectiveness on dimensional change, they have newly arisen problems, i.e., increase of fog (Dmin), fluctuation of light exposure time to PS plates and so forth, which are caused by storage or light irradiation of treated films.
An object of the present invention is to provide a heat-developable photosensitive material of improved fluctuation of photographic performance (sensitivity, Dmin) arisen from fluctuation of development temperature condition (temperature, time) and storage period after heat development, more specifically, to provide a heat-developable photosensitive material more stably affording ultrahigh contrast characteristics for photomechanical process, and to provide a heat-developable photosensitive material of excellent dimensional stability. Another object of the present invention is to provide a heat-developable photosensitive material for photomechanical process, in particular, for scanners and image setters, which affords an image with low fog, little increase of fog and little fluctuation of sensitivity during storage before light exposure and an image of high Dmax (maximum density) suitable for use in photomechanical process, and which can be performed by applying an aqueous coating solution which is advantageous in view of environmental protection and costs
According to the present invention, there is provided a heat-developable photosensitive material, wherein the photosensitive material comprises, on a support, an image-forming layer containing at least (a) non-photosensitive organic silver salt, (b) photosensitive silver halide, (c) a reducing agent, and (d) a binder, and a protective layer on the image-forming layer, polymer latexes are used as binders of the image-forming layer and the protective layer, and the photosensitive material further comprises, on the image-forming layer side, (e) a nucleating agent and (f) one or more compounds represented by the following formula (1). 
In the formula (1), Z1 and Z2 each independently represent a halogen atom, X1 represents a hydrogen atom or an electron withdrawing group, Y1 represents xe2x80x94COxe2x80x94 group or xe2x80x94SO2xe2x80x94 group, Q represents an arylene group which may have a substituent or a divalent heterocyclic group which may have a substituent, L represents a linking group, W represents carboxyl group or a salt thereof, slufo group or a salt thereof, phosphoric acid group, hydroxyl group, a quaternary ammonium group, or a polyethyleneoxy group, and n represents 0 or 1.
The nucleating agent preferably consists of one or more of a substituted alkene derivative represented by the following formula (2), a substituted isoxazole derivative represented by the following formula (3), and an acetal compound represented by the following formula (4). 
In the formula (2), R1, R2 and R3 each independently represents a hydrogen atom or a substituent, and Z represents an electron withdrawing group or a silyl group. In the formula (2), R1 and Z, R2 and R3, R1 and R2, or R3 and Z may be combined with each other to form a ring structure.
In the formula (3), R4 represents a substituent.
In the formula (4), X and Y independently represent a hydrogen atom or a substituent, A and B independently represent an alkoxy group, an alkylthio group, an alkylamino group, an aryloxy group, an arylthio group, an anilino group, a heterocyclyloxy group, a heterocyclylthio group or a heterocyclylamino group, and X and Y, or A and B may be combined with each other to form a ring structure.
Preferably, the support has, on both surfaces, one or more undercoat layers which have a thickness of 0.3 xcexcm or more (total thickness for each surface) and contain a vinylidene chloride copolymer containing at least 70% by weight of repeating units of vinylidene chloride monomers.
Preferably, the nucleating agent consists of one or more compounds represented by the formula (A) or (B). 
In the formula (A) and (B), Z11 and Z12 each represent a nonmetallic atomic group which can form a 5- to 7-membered ring structure including Z11 and Z12, Y11 and Y12 each represent xe2x80x94C((xe2x95x90O)xe2x80x94 group or xe2x80x94SO2xe2x80x94 group, and X11 and X12 each represent hydroxyl group (or a salt thereof), an alkoxy group, an aryloxy group, a heterocyclyloxy group, mercapto group (or a salt thereof), an alkylthio group, an arylthio group, a heterocyclylthio group, amino group, an alkylamino group, an arylamino group, a heterocyclylamino group, anacylamino group, a sulfonamide group, or a heterocyclic group. Y13 represents a hydrogen atom or a substituent.
Preferably, the heat-developable photosensitive material of the present invention preferably contains, on the side of the support provided with the photosensitive silver halide, at least one compound represented by the following formula (Z). 
In the formula (Z), M represents a hydrogen atom or a k-valent cation, and R represents a substituent. m represents an integer of 1-4. When n is 2 or higher number, a plurality of R maybe the same or different. k is an integer of 1 or higher, and when M is a hydrogen atom, k is 1.
Preferably, the heat-developable photosensitive material of the present invention has a film pH of 6.0 or less.
Preferably, the heat-developable photosensitive material of the present invention further contains, on the side of the support provided with the photosensitive silver halide, at least one compound represented by the following formula (5).
Z11xe2x80x94SO2SMxe2x80x83xe2x80x83(5)
In the formula (5), Z11 represents an aliphatic hydrocarbon group, an aryl group or a heterocyclic group, and M represents a cation.
Preferably, the photosensitive silver halide is subjected to spectral sensitization in the range of 750-1400 nm.
Preferably,the polymer latex of the image-forming layer comprises a polymer latex having a glass transition temperature of xe2x88x9230 to 40xc2x0 C. in an amount of at least 50% by weight of